Pyrazolotriazoles, such as those described herein are useful magenta couplers for photographic products. However, they are difficult to synthesize. Only a few synthetic routes are known. One of the preferred synthetic routes involves preparation of the triazolothiadiazines 1 and subsequent desulfurization reaction to give the pyrazolotriazoles 2. The triazolothiadiazines 1 can be prepared in two ways; the first, by reaction of 4-amino-5-mercapto-3-substituted(R)-1,2,4-triazoles (4) with alpha-haloketones, or the second, by reaction of 2-hydrazino-5-substituted-(R')-1,3,4-thiadiazines (5) with acyl halides and subsequent dehydrative ring closure. Both the triazoles 4 and the thiadiazines 5 are readily available from thiocarbohydrazide; ##STR4## The desulfurization of these triazolothiadiazines 1 to the pyrazolotriazoles 2: ##STR5## is effected in two steps; the first, a ring contraction reaction of 1 by heating in acetic anhydride to give 1-acetyl-7-acetylthio-3,6-disubstituted-1H-pyrazolo[5,1-c]-1,2,4-triazoles (6) and, the second, hydrolysis of acetyl groups and desulfurization at the same time with hydrochloric acid to give the desired 2. ##STR6## Although this is the most attractive and practical method for desulfurization among those available, there are several drawbacks in using this as a manufacturing process. The first ring contraction reaction is usually clean and does not render any problem except long reaction time. In fact, the reaction mixture is clean enough to be used in the next step without isolation of 6. However, the subsequent reactions are not straight-forward. The hydrolysis and desulfurization reactions with hydrochloric acid generate not only elemental sulfur as by-product but also many sulfur-containing organic impurities. Among them are two major impurities identified as thione 8 and disulfide 9. These oxidized forms of mercapto intermediate 7 seem to result by the action of elemental sulfur formed during the reaction of 7.
Not only elemental sulfur, but also the sulfur-containing organic impurities are considered detrimental. They can interfere with subsequent reaction steps, e.g. a catalytic hydrogenation of a nitro group on one of the groups R or R' in the above formulae. Also, sulfur is a potential fogger in photographic systems.
Because the process of this invention makes much smaller amounts of these detrimental impurities, and is straight-forward and readily carried out, it is considered to be a significant advance in the art.